76 MOTION THE TEST OF ACTION. 



evaporate until the salt crystallizes or forms into 

 little solid lumps, there is motion in the case; 

 and we can trace the process backward till we find 

 motion, and motion alone, for which we cannot 

 account. The invisible atoms of salt which were 

 scattered through the clear brine, must move to- 

 wards each other in order to form the little crys- 

 tals ; and the law which regulates their invisible 

 march is as perfect and as uniform as that which 

 regulates the motion of the earth upon its axis or 

 round the sun ; for, unless in cases where we can 

 find a cause preventing them, those crystals always 

 assume the same form. The formation of the 

 crystals is one motion, and it is a very important 

 one ; because, as there is no other substance which 

 crystallizes under exactly the same circumstances 

 as common salt, it is by knowing and bringing 

 about that small and invisible motion that we are 

 enabled to give a pure and wholesome relish to our 

 food ; for even common salt, as it exists in nature, 

 is mixed with magnesia and sulphur, and other 

 ingredients which render it unpalatable and un- 

 wholesome. 



The previous state of the process is also motion. 

 A certain quantity of water, having a certain de- 

 gree of heat, is necessary for separating the natu- 

 ral salt into particles so small as to be invisible ; 

 and the quantity that can be dissolved in boiling 

 water is far greater than that which can be dis- 

 solved in cold water. Now it is the property of 

 water that it begins to boil at two hundred de- 

 grees of the common thermometer, or a little less 

 or more according to the state of the atmosphere. 

 When that is light, boiling water is a little cooler, 

 and when heavy, it is a little warmer ; but the va- 



